Permanent magnetic pulley



Dec. 29, 1964 .1. J. FERRIS ETAL PERMANENT MAGNETIC PULLEY 2 Sheets-Sheet 1 Filed May 21, 1962 Dec. 29, 1964 J, J. FERRIS ETAL PERMANENT MAGNETIC PULLEY 2 Sheets-Sheet 2 1/1/Il/ Il ill 11/4 United States Patent Ofilice greases Patented Dec. 29, 1964 This invention relates generally to magnetic attractors and more particularly to permanent magnetic pulleys.

Apparatus of the magnetic type for separating or segregating magnetizable and non-magnetizable materials from a mixture or stream of such materials are known. Magnetic attractors constructed as magnetic separators and magnetic pulleys utilize electromagnets and permanent magnets, however, because of the inherent expense and operational difficulties of electromagnetic attractors permanent magnets have replaced the electromagnets in many types of separators and attractors.

Magnetic pulleys with permanent magnets have heretofore made use of ceramic permanent magnets. These magnetic pulleys, however, are highly inefficient in that the effective energy is a very reduced part of the total available flux energy developed by the magnets in the apparatus pole pieces and has not been effectively used to provide the total or maximum energy available for separating magnetic and non-magnetic materials. Known magnetic pulleys making use of the high coercive force of magnetic wafers made of ceramic permanent magnetic material make use of annular pole pieces which have their internal diameters relatively large with respect to the outer diameters so that the flux leakage is substantially maximized thereby greatly reducing the effectiveness of the ceramic permanent magnets employed therein and requiring more magnets, and, therefore, a larger, more expensive pulley, to develop a force field of flux of a given coercive force.

It is a principal object of the present invention to provide a permanent magnet construction optimizing the flux density for unit area in the pole pieces thereof.

Another object is to provide a pulley construction resulting in a minimum number of magnets to develop a selected flux density therebyreducing the cost of construction and minimizing the size of the pulley.

Still another object is to provide a very efiicient pulley increasing the quality of segregating that it can accomplish and being capable of being operated at greater rotational speeds thereby increasing the quantity of non-magnetizable and magnetizable materials that it can segregate in unit time.

A feature of the present invention is the provision of new and novel magnet constructions comprising a plurality of magnet assemblies of similar magnetic units in the form of annular discs, made, for example, of a magnetic ceramic material and disposed between pole pieces forming poles of alternate polarity. The discs or magnetic units each have a greater length and width or diameter dimension than thickness with opposite major faces defining the thickness dimension. The magnetic units within each magnet assembly are arranged contiguous to each other with face-to-face relationship of the units and between major faces of two successive pole pieces. The magnet units are permanently magnetized in the same direction in each assembly and in final assembly the direction corresponds to a direction substantially normal to the opposite faces defining the thickness dimension and normal to the major faces of the pole pieces and parallel to the axis of the pulley.

A principal feature is that the pole pieces of the magnetic pulley, according to the invention, areof a magnetically permeable material and have a central opening through which a non-magnetic shaft extends for rotating the magnetic pulley. The central opening has a minimum inside diameter with respect to the outside diameter thereby optimizing flux density in the various embodiments of the magnetic pulley of the invention.

Other features and advantages of the magnetic pulley, in accordance with the present invention, will he better understood as described in the following specification and appended claims, in conjunction with the following draw ings, in which:

FIG. 1 is an axial section of a first embodiment of a permanent magnetic pulley according to the invention;

FIG. 2 is an end veiw of the magnetic pulley illustrated in PEG. 1 with portions cutaway;

FIG. 3 is a longitudinal axial section of a second embodiment of a magnetic pulley according to the invention; and

FIG. 4 is an end view of the magnetic pulley illustrated in FIG. 3 with portions cutaway thereon.

In the drawing, FIG. 1, a permanent magnetic pulley 10 used as a magnetic separator is shown. The magnetic pulley Jill is installed, for example, as the pulley in a discharge position of a conveyor, not shown, transporting a stream of magnetizable and non-magnetizable material. The pulley it'll rotates in timed relationship with the longitudinal travel of the conveyor belt, not shown. The bulk material carried on the conveyor belt includes magnetizable material which as it approaches the influence of the magnetic field of the magnetic pulley 10 is responsive to the magnetic attraction of the magnetic pulley 10 from the underside of the conveyor belt. As the non-magnetic material flows over the magnetic pulley it is discharged in a trajectory because it is not influenced by the magnetic held and has speed and mass and is influenced by gravity. The magnetic materials are transported around the pulley with the belt beyond the area of discharge of the nonmagnetic materials. The magnetized material is discharged from the lower run of the belt as the material moves away from the magnetic field of the magnetic pulley. The magnetically responsive material once out of the influence of the magnetic field drops off in response to the force of gravity into a suitable container, chamber, hopper or the like and separation of the magnetic and non-magnetic material has taken place.

The pulley Ill comprises a non-magnetic shaft 12 coaxial with the axis of rotation of the pulley 10. The pulley is pivotally mounted on the shaft for rotation and operation as described above. Three annular, magnetically permeable pole pieces 14, 15, 16 are mounted spaced axially on the shaft 12 and define an axial space between each pair of them. The pole pieces are made, for example, of steel or soft iron and are keyed to the shaft by keys 17, 18, 19 disposed in a keyway of the shaft as illustrated.

The embodiment illustrated in FIG. 1 comprises two magnet assemolies 2G, 21 each disposed between two successive pole pieces. The magnets 20, 21 are each made of a plurality of annular magnetic units, designated 1, 2, 3, 4 in magnet 243. The other magnet 21 is similariy constructed. The magnetic units have central openings 23, 24 through which the shaft 12 passes and have opposite major faces defining their thickness dimension.

The magnetic units are arranged so that their major faces are in an intimate facetrrface relationship and the units extend axially in the axial spaces formed between successive pole pieces. Each magnetic unit has a greater length or diameter than thickness dimension, Units within each magnet assembly have permanent magnetization in the same direction through the thickness dimension. The direction of magnetization corresponds to the magnetization in a direction substantially normal to the surfaces defining the opposite major faces defining the The pulley illustrated in FIG. 1 comprises annular heads 39, 31 at opposite ends of the pulley made of nonmagnetic material and secured to the outer faces of the two end pole pieces 14, 16 with a plurality of screws 34 angularly disposed in bosses in rims or flanges 35, 36 extending radially inwardly at an inner end of the respective heads as illustrated in FIGS. 1 and 2. A non-magnetic shell 33 formed as a tubular element extends between the heads 3'1), 31 circumferentially of the magnetic units and the three pole pieces 14, 15, 16 and is secured to the end pole pieces by a plurality of angularly spaced, fiat-head, bolts or screws 39 so that a smooth elongated pulley is formed for engaging a conveyor belt, not shown, operative as described heretofore. The shell and the heads are made, for example, of brass or stainless steel.

The construction of the permanent magnets illustrated in FIGS. 1 and 2 is such that the magnetic units have opposite polarity on their major faces as illustrated in FIG. 1. Thus the central pole piece is a south pole and the end pole pieces l4, 16 are north poles. Each pole piece has a central opening whose internal diameter is of a minimum dimension with respect to the outside diameter thereof. The surfaces defining the inside diameters make contact with the shaft 12 circumferentially thereof. Thus two magnetic loops are formed between the end pole pieces and the middle pole piece 15. Substantially all the flux developed by each of the magnets, 20, 21 passes through the two pole pieces holding the magnetic units thereof in a compressed intimate face-to-face relationship among themselves and the major faces of the two successive pole pieces. The two loops of flux thereby formed have maximum density per unit area on the outside diameter surfaces of the pole pieces. The central pole piece 1.5 is, of course, made thicker than the end pole pieces since the two flux loops pass through it. The flux loops pass through the shell and the flux is effective along the axial length of the pulley circumferentially thereof so that a conveyor belt surface transporting the material to be segregated has the segregating flux applied across its full width with maximum possible density throughout the full width of the belt so that all the material thereon is subjected to the effect of the magnetic pulley and an optimum segregating force.

The magnetic units 1-4 are all alike annular elements with coaxially disposed central openings and have a same inside diameter and the same outside diameter. There is no need for the magnetic units to make contact with the shaft and are disposed radially thereto as desired. It will be understood by those skilled in the art that the configuration and arrangement of the elements of the pulley according to the invention permit construction of magnetic pulleys of different axial lengths and by increasing or decreasing the number of magnetic units in each magnet assembly.

A second embodiment of the magnetic pulley and permanent magnets therefor is illustrated in FIGS. 3 and 4. In this construction a plurality of permanent magnet assemblies of the type heretofore described are disposed with the centers of their magnetic units radially spaced equally from the axis of rotation of a pulley 5% as described below. The pulley 50 comprises three annular, magnetically permeable, axially spaced pole pieces 52, 53, 54 mounted for rotation on a shaft 55 similarly to those heretofore described. Between successive pole pieces is disposed a plurality of magnet assemblies. Six magnet assemblies 56-61 are disposed between the central pole piece 53 and the outer pole piece 54. A similar number are disposed between the pole pieces 53 and 52 but only two magnets 63, 64 are shown. It being understood that for each magnet or magnet assembly disposed between the middle pole piece and the outer pole piece 54 there is a correspondingmagnet assembly axially spaced therefrom between the center pole piece 53 and the end pole piece 52. The magnet assemblies are arranged in pairs, for example magnet assemblies 56 and 63 are a pair. The pairs of magnets are disposed coaxially and are held with six tie rods, for example, tie rods 66, 67, threaded at both ends on which are threaded nuts outwardly of the end pole pieces. The tie rods are disposed radially of the shaft 5% an equal radial distance and are spaced angular-1y equidistant.

Wooden spacers 69-72 are disposed circumferentially of each of the tie rods extending axially through central openings in eight annular or disc magnetic units forming each magnet. The magnetic units are of the typeof the first embodiment and designated L8 as illustrated, and each magnet has the magnetic units therein arranged as described above. The entire assembly of pole pieces and permanent magnets are positioned axially on the shaft 55 by positioning collars 75, 76 held in fixed axial positions by set screws '75, 76.

The pulley comprises heads 78, 79 at opposite ends thereof secured to the end pole pieces 52, 54 with bolts 86 in a plurality of bosses in flanges 81, 82 on the heads extending radially inwardly on the inner ends of the two heads '78, 79 respectively. The headsare made of a nonmagnetic material, for example, brass or stainless steel. A thin shell 84 formed as a tubular element is disposed circumferentially around the permanent magnets and pole pieces and secured to the end pole pieces with angularly spaced non-magnetic screws 85.

In this manner a simple dynamically balanced magnetic pulley is formed in which two loops of lines of flux extending circumferentially of the pole pieces are formed between the pole piece 52 which is a north pole and pole piece 53 which is a south pole and between the central or south pole piece 53 and the outer or end pole piece 54. The magnetic pulley 5d provides a unit that can be easily assembled and has high coercive attractive force because it makes optimum use of the coercive force of the magnetic flux and reduces flux leakage to a minimum so that maximum fiuxdensity is obtained to develop the maximum possible coercive magnetic force to attract the magnetizable material to the belt, not shown, on the pulley with a minimum size pulley. the art that the pole pieces 52-54 have minimum external diameters and the internal surfaces make contact With the shaft circumferentially. The magnet units 1-8 in each magnet assembly are disposed in a radial position governed by desired dynamic characteristics and the attractive force of the magnet is unaffected by their radial position.

In both embodiments of the invention the magnet units have arcuate outer surfaces and are made as annular discs. It will be understood that the shape of the magnetic units is unimportant. However, discs can be easily made and provide for interchangeability since the discs can be used to make pulleys similar to the first embodiment and the same type of discs can be used to make pulleys similar to the second embodiment. For example, the thicker discs illustrated in FIG. 1 can be mounted in place of the thinner discs illustrated in FIG. 3 and a lesser number of pairs of assemblies employed.

The permanent magnet units are preferably made of a non-metallic material comprising magnetic ceramic material, for example, barium fern'tes. These ceramic materials can be magnetized in the direction of the thickness dimension of the unit and have a high degree of permanency of magnetization. While the magnet units as disclosed preferably have a greater length and width dimension, a greater diameter, than thickness, it is to be understood that the thickness can be greater than the other dimensions. The arrangement-in such a case is It will be noted by those skilled in the same as described with respect to the embodiments illustrated. Because of the arrangements of the units the assemblies make optimum use of the flux thereby requiring smaller magnet constructions to accomplish the same amount of work as other known constructions.

Moreover, for a given size pulley with a given number of magnetic units as against known constructions the magnet pulley according to the invention can sort out a greater amount of material since operational speeds can be increased in view of the optimum use of the magnetic lines of force available to the pole pieces.

It Will be noticed that the magnetic pulley according to the invention permits construction of pulleys of various diameters and lengths. While the second embodiment of the invention shows one intermediate pole it is possible to use any number of intermediate poles so long as the successive pole pieces are of alternate polarity whereby more than two loops of magnetic lines of force will be developed and the loops will be coactive to carry out segregation on a pulley longer, for example, than those shown in the drawing. The diameters of the pole pieces and magnetic units can be of any suitable dimension. The number of magnet assemblies or units within each assembly can be preselected at any desired number. The arrangement and configuration of the elements of the invention is such that any number of possible lengths or diameters of pulleys with fields of same or different coercive force can be constructed.

The magnetic pulley provides simple means for holding the magnetic units in the magnets in intimate relationship under compression by the use of positioning collars in both embodiments and long through-rods in conjunction with the rods in the second embodiment. The through-rods also function to assist in holding the magnetic elements in position radially in conjunction with spacers so that the apertures in the discs can be kept to a minimum size and the pulley can be operated at optimum rotational speeds including higher speeds than heretofore possible. The mounting of the magnetic discs coaxially with the shaft in the first embodiment likewise permits construction of pulleys operable at high speeds. In all embodiments the fields of optimum, maximum coercive force, as indicated heretofore, permit optimum use of the new mechanical arrangement of elements for operation at optimum productive speeds.

While preferred embodiments of the magnetic pulleys according to the invention have been shown and described, it will be understood that many modifications and changes can be made within the true spirit and scope of the invention.

What we claim and desire to secure by Letters Patent is:

1. A magnetic pulley comprising, in combination, a plurality of axially spaced, magnetically permeable, annular pole pieces alternately of opposite polarity, said pole pieces having major faces, a plurality of permanent magnets for magnetic induction of said pole pieces, each disposed intermediate two successive pole pieces, each magnet comprising a plurality of alike, circumferentially spaced, annular magnetic units mounted between said pole pieces, said magnetic units in each magnet having opposite major faces and arranged with said major faces in a. faceto-face relationship in intimate contact, each mag netic unit having a greater diameter than thickness, endmost of said magnetic units in each magnet having major faces in intimate contact individually with major faces of individual ones of said pole pieces, said units having permanent magnetization in the same direction through the thickness dimension, said direction of magnetization corresponding to magnetization in a direction substan tially normal to the opposite major faces defining said thickness dimension, and parallel to the axis of rotation of said pulley, means mounting said pole pieces and magnetic units for rotation comprising a non-magnetic shaft fixed to said pole pieces extending axially through said pole pieces, said pole pieces and said magnetic units being disposed coaxially with said shaft, said pole pieces having centrally disposed surfaces defining a central opening through which said shaft extends, said centrally disposed surfaces defining said opening extending circumferentially of said shaft and making contact circumferentially with the surface of said shaft, said central opening having a minimum possible diameter relative to the outside diameter of said pole pieces, a non-magnetic tubular shell fixed for rotation with said shaft disposed axially over said magnets and pole pieces and circumferentially thereof, and means for holding said pole pieces and magnetic units in position on said shaft and said magnetic members with axially directed compression forces applied thereto.

2. A magnetic pulley according to claim 1, in which the last-mentioned means comprises non-magnetic collars disposed axially outwardly of said pole pieces positionable variably axially on said shaft developing compressive forces between said pole pieces.

3. A magnetic pulley according to claim 1, in which said last-mentioned means comprises a plurality of through-rods extending axially individually through a plurality of said magnets disposed coaxially and extending axially through the magnetic units comprising said coaxial magnets and through successive pole pieces, each of said through-rods having at least one end threaded and means threaded on said threaded end for applying said compressive forces.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A MAGNETIC PULLEY COMPRISING, IN COMBINATION, A PLURALITY OF AXIALLY SPACED, MAGNETICALLY PERMEABLE, ANNULAR POLE PIECES ALTERNATELY OF OPPOSITE POLARITY, SAID POLE PIECES HAVING A MAJOR FACES, A PLURALITY OF PERMANENT MAGNETS FOR MAGNETIC INDUCTION OF SAID POLE PIECES, EACH DISPOSED INTERMEDIATE TWO SUCCESSIVE POLE PIECES, EACH MAGNET COMPRISING A PLURALITY OF ALIKE, CIRCUMFERENTIALLY SPACED, ANNULAR MAGNETIC UNITS MOUNTED BETWEEN SAID POLE PIECES, SAID MAGNETIC UNITS IN EACH MAGNET HAVING OPPOSITE MAJOR FACES AND ARRANGED WITH SAID MAJOR FACES IN A FACE-TO-FACE RELATIONSHIP IN INTIMATE CONTACT, EACH MAGNETIC UNIT HAVING A GREATER DIAMETER THAN THICKNESS, ENDMOST OF SAID MAGNETIC UNITS IN EACH MAGNET HAVING MAJOR FACES IN INTIMATE CONTACT INDIVIDUALLY WITH MAJOR FACES OF INDIVIDUAL ONES OF SAID POLE PIECES, SAID UNITS HAVING PERMANENT MAGNETIZATION IN THE SAME DIRECTION THROUGH THE THICKNESS DIMENSION, SAID DIRECTION OF MAGNETIZATION CORRESPDING TO MAGNETIZATION IN A DIRECTION SUBSTANTIALLY NORMAL TO THE OPPOSITE MAJOR FACES DEFINING SAID THICKNESS DIMENSION, AND PARALLEL TO THE AXIS OF ROTATION 